I. Field of the Invention
The present invention relates to an electronic multi-range step resistor with analog adjustment.
II. Description of the Prior Art
A significant advantage of an electronic step resistor for adjustment of a timing relay in comparison to the known mechanical timing relays is the reduced return time of the timing unit and an always constant precision for the time adjustment in the entire timing range, since the inevitable coupling errors, in case of the mechanical timing relays, are here nonexistent. In addition, electronic timing relays are already advantageous for special fields of application because they make possible time adjustments, that is, the delay of switch positions, down to the range of 10 milliseconds. They can be operated within a very large frequency range independent of the frequency of the power source. Operation with direct current is possible with only little effort.
The objective for the construction and the production of such electronic step resistor for adjustment of timing relays is by far different in comparison with the mechanical timing relays since the electronic step resistor does not use any electromechanical power source and therefore does not use any moving parts, such as the synchronous motor, the reducing gear, coupling devices, and a timing wheel such as are normally used for mechanical timing relays.
Electronic timing relays have been known for some time in the form of versions, such as the condenser relays, as well as in the form of versions with electronic tubes, or in the form of more modern versions which are completely transistorized. Especially popular are electronic timing relays; for instance, wipe relays, blink relays, and impulse supply units. The timing transient for electronic time relays is preferably supplied by means of RC units which will then define the desired delay time. Condenser relays are mainly characterized by the fact that the resistance in the RC unit is small, whereas condensers of high capacity are used.
In addition to the single-range timing relays, such as for the electromechanical timing relays or for the electronic timing relays, multi-range relays are also known. In case of these relays, individual time ranges, for instance up to one second, ten seconds, one minute, ten minutes or one hour, can be selected by means of a switch; and with another turning knob a continuous time adjustment can be chosen within each of the preselected ranges. The switch for the time ranges activates a selection switch with which, for instance, different resistors can be looped into the RC unit or taken out of the RC unit, and the turning knob is connected with a potentiometer by means of an access or a shaft which continuously varies the fixed resistors in the given range which was selected by means of the switch. Both knobs necessary for operation, that is to say, the switch and the turning knob, are located at the front of the electronic timing relay at a distance therefrom. The general trend for the miniaturization of such devices brought about housing dimensions in recent years which necessitated the construction of operating knobs which were very small with regard to their diameter and which operating knobs had to be positioned relatively close to each other. In this way, the corresponding scales had to be constructed smaller and smaller which resulted necessarily in a larger error of adjustment. This adjustment error, for one thing, is caused by the unfavorable optical readability of the data to be adjusted on the small scale and, on the other hand, by the unfavorable manual handling of the small operating knobs which are located in close proximity to each other.
The historical development continued in such a way that as first analog adjustment units were used; and after miniaturization had taken place, due to the large adjustment errors, a change was made towards digital adjustment possibilities by means of (dial) decade switches or similar equipment. However, this caused considerable, additional cost.
On the other hand, mechanical multi-range timing relays are known in which the switch for the individual time ranges is located centrally on top of the turning knob for the continuous time selection within the time range, which turning knob covers a large portion of the frontal plate and which transparent turning knob overlaps the scales. A location in such a way enables not only an especially easy and accurate manipulation of both of the knobs, but it also makes optimum or maximum use of the available vertical area of the frontal plate of the time relay for the manual operating devices. The location of the scale underneath the transparent turning knob does not create any difficulties with regard to space. Even for miniaturized relays, the scale can be read even from a considerable distance due to its possible size.
The mentioned location of one of the operating knobs above the other for a multi-range timing relay is possible for mechanical time relays since here the switch for the individual time ranges activates a system of gears which couple various different reduction gear steps of a reduction gear to the synchronous motor which activates the mechanical time relay, and the turning knob for the continuous time selection controls the timing reel.
III. Prior Art Statement
The above description of the prior art, in the opinion of applicant, represents the closest prior art of which applicant is aware.